The invention relates to optical data storage. More specifically, the invention relates to a method for writing data to an optical storage medium such as a DVD or a CD. xe2x80x9cRead/writexe2x80x9d optical discs include optical discs that allow new data to be written only once and optical discs that allow new data to be written many times. A DVD+RW disc is an example of a read/write disc that allows new data to be written many times. xe2x80x9cRead/writexe2x80x9d drives can write data to xe2x80x9cread/writexe2x80x9d optical discs. A read/write drive typically has a read mode of operation and at least one of the following write modes of operation: a write-append mode and an insert-edit mode. The write-append mode allows new data to be appended to previously written data on the read/write disc, and the insert-edit mode allows previously written data to be overwritten with new data.
When writing new data to a read/write disc, it is desirable not to create a frequency or phase discontinuity between the previously written data and the new data. The read/write drive might not be able to tolerate such discontinuities during read back of the previously written data and the new data. During readback, the discontinuities might cause problems for clocks and data recovery circuitry. Consequently, the discontinuities might render portions of the read/write disc effectively unreadable by the read/write drive.
The problems resulting from these discontinuities may be overcome by the use of xe2x80x9cedit gapsxe2x80x9d (also known as xe2x80x9csplice areasxe2x80x9d and xe2x80x9cbuffer zonesxe2x80x9d). The edit gaps separate the previously written data and the new data. A frequency or phase discontinuity might arise from an edit gap following a block of the previously written data. During readback of the previously written data and then the edit gap, the clocks and data recovery circuitry might become unstable. However, the edit gap allows sufficient time for the clocks and data recovery circuitry to recover before the newly written data is read back.
However, the use of edit gaps has its drawbacks. Storage capacity of the read/write disc is reduced because data is not stored in the edit gaps.
Moreover, the edit gaps might render portions of the read/write disc unreadable by existing read-only drives. Older read-only drives that were developed prior to newer generation read/write drives might not be capable of processing the edit gaps. Unless an existing read-only drive is somehow modified to navigate past the edit gaps, it will have difficulty reading the data stored on the read/write disc.
There is a need for a read/write drive that does not rely upon edit gaps to overcome the problem arising from discontinuities between previously written data and newly written data.
This need is met by the present invention, which may be regarded as a method of writing a block including new data to a read/write medium. The method includes locating an edit bit in a block that has already been written to the medium, and writing the new block to the disc, beginning or ending at the edit bit.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.